From a large dataset of aftershocks in the rupture area of the Mw=8.0 1995 Antofagasta earthquake we derived the spatial distribution of hypocenters and a b-value map along the fault plane. We further examined various focal mechanisms of the aftershock sequence. The b-value distribution on the fault plane clearly indicates the heterogeneity of the rupture area. We found a positive correlation between the b-value variations and the main shock source time function determined by Delouis [1996> where zones of high b-value are related to high slip. With these results we propose to have found evidence for the segmentation of the fault plane and suggest that the mapped inhomogeneities could have played the role of asperities prior to the main shock rupture. ¿ 2000 American Geophysical Union